Thank you ahead of time for reading this and any responses.

The project I'm working on is in C11, using mostly standard and POSIX libraries, and the Xlib and XCB, additionally, Lthreads-a lightweight threading library. Alternately GNU Pth could serve for the lightweight threading.

Currently it's fine just using Ubuntu 15.04 and also 14.04. Probably it will be switched to something less pretty. Suggestion for distro's which will run on big, old, multi chip, multi core servers/workstations would be welcome, too. Bearing in mind that this is for research, not games or media production. It would be best to run an x server on the same machine.

At this point it needs to move from a couple of networked i5 and similar AMD based machines to a larger, AMD64 aka x64 based, massively multiprocessor system.

NUMA is not just OK, it is preferred. It is not needing ultra-speedy execution, just a lot of cores (16 +) spread across multiple chips. In the future it will be largely I/O bound, residing on several large-ish machines.

This is not primarily a graphics application, does not use 3D, and Xlib and XCB serve it perfectly-no need for GTK+. Qt, Cairo, etc.

All that's, graphics-wise is available from the built in graphics on most machines For example: ATI ES1000 -16mb graphics would probably suit it just fine. If not, it can be networked to a nice cheap computer already running an X Server. Refresh rates as low as 20fps are good, 30fps is great. Using nothing but graphics primitives and events. HD resolution rather than speed is important.

This is a low budget project and end of life chips are fine so long as they are 64 bit, etc., as I've already described.

I've found what I THINK are acceptable machines at this green computing, respectable company, in the right price range. They certainly seem adequate.

So, IBM System x3850 M2? Maybe a Dell Power Edge 900? Hp Proliant? I'm thinking the IBM might be best. It's local pickup and not too expensive so it needn't be the absolute best-adequate is more than adequate. The final application will have to run on a heterogeneous, motley crew of computers.

If you've read all of this, thank you for your patience!

For the suggestions, the usual suspects are what I'd recommend. AKA - CentOS, Debian, Slackware.

Thanks for the suggestions, but the thing I'm asking about is hardware.

In retrospect, it was silly of me to mention much at all about the distro I'm using. My question was for hardware suggestions.

I'll probably go with the IBM x3850 unless I find a surprisingly underpriced Power Edge 900.